[en] Measurements of the depth-distribution of ²¹⁰Pb and ¹³⁷Cs activities, and radiocarbon ages in sediment box cores from the Laurentian Trough were made to determine modern sedimention rates in this deep coastal environment. Estimates of biological mixing coefficients (D_b) were calculated using the depth-distribution of excess ²²⁸Th and ²³⁴Th activities for the top 2-5 cm of the sediment. Although these surficial D_b's (10^-7 to 10^-8 cm²/s are low for coastal sediments, they are sufficient to cause serious bioturbational errors in the slopes of uncorrected radionuclide data. Using a model of depth-zoned bioturbation, and estimates of subsurface D_b an order of magnitude smaller, sedimentation rates of several mm/yr are arrived at. These are in good agreement with direct sedimentation rate measurements obtained using sediment traps